A geophysical survey of the East China Sea, Yellow Sea, and Ryukyu Island arc and trench was conducted during October-November 1968, by the U. S. Naval Oceanographic Office with participation by scientists from ECAFE member nations. More than 12,000 km of continuous seismic reflection profiling, magnetic, and bathymetric data were recorded.

The distribution of sedimentary strata appears to be controlled by a series of NE-SW trending ridges that dam and separate large sediment-filled depressions. The sediments were derived mainly from the large section of Chinese mainland drained by the Yellow and Yangtze Rivers. The Fukien-Reinan massif (between southeastern Korea and the mouth of the Yangtze River) consists of Precambrian to Mesozoic rocks uplifted during the Mesozoic Era. It dams a thick sequence of Paleogene and Neogene sedimentary rocks in the Yellow Sea. A ridge of folded sedimentary and igneous rock near the edge of the continental shelf is probably the sea-floor expression of the Taiwan-Sinzi folded zone which began to be active during Paleogene time. Approximately 1 million cu km of Neogene sedimentary strata (at aining a thickness of probably at least 5 km) and some Paleogene sedimentary rocks are dammed by this ridge. An extensive unconformity separates Neogene from Paleogene strata beneath the Yellow Sea and the continental shelf. The Neogene unit is generally undeformed, whereas the Paleogene unit shows evidence of structural deformation followed by erosion. Beyond the continental shelf the Ryukyu Ridge, composed of volcanic rocks, folded Paleogene and faulted Neogene strata, and Paleozoic and Mesozoic igneous and metamorphic rocks, has dammed a belt of sedimentary strata of probable Neogene age in the Okinawa Trough. Sediment fill in the trough exceeds 1.2 km in thickness and contains many internal reflectors that may be turbidite sand layers. Abundant faults and complex folds beneath the si e slopes suggest fault origin of the Okinawa Trough. Another dam halfway down the eastern edge of the Ryukyu Ridge has trapped additional sediments to form a broad terrace. The Ryukyu Trench at the foot of the Ryukyu Ridge contains zero to about 600 m of sediment and terminates against Taiwan in a trench-transform fault junction.

Sedimentary strata beneath the continental shelf and the Yellow Sea appear to have a high potential for oil and gas. Much of the continental shelf north of Taiwan has sedimentary thickness exceeding 2 km, most of which is believed to be of Neogene age, as are the oil-producing strata on Taiwan. Present information suggests that the strata are dominantly shale but with some interbedded sandstone zones that serve as acoustic reflectors. Numerous anticlines, faults, and unconformities were recorded. Our reconnaissance study indicates that detailed seismic surveys are warranted and that eventual test drilling will be required to establish the potential for oil and gas in the region.